Lead-in construction for electrical devices



June 15, 1948. D. o. SCHWENNESEN 2,

LEAD-IN CONSTRUCTION FOR ELECTRICAL DEVICES Filed Dec. 11. 1944 m JW WMPZ I 4 J 5 Q 3 MD 5 Q y 0 Patented June 15, 1948 LEAD-IN CONSTRUCTION roa ELECTRICAL navrcns Donald 0. Schwenncsen, Chicago, Ill., assignmto Essex Wire Corporation, Detroit, Mich, a

corporation of Michigan Application December 11, 1944, Serial No. 567,611

4 Claims. (Cl. 174-18) 1 This invention relates to an electrical apparatus and particularly to lead-ins for any electrical device which is potted or cased for sealing. In many devices such as transformers, reactors,

condensers and the like, it is often necessary to seal the same within a container for protection against weathering, moisture and other corrosive influences found in various climates. As a rule, such devices may be impregnated with and surrounded by oil or wax as an added precaution against voltage breakdown as well as to prevent access of moisture to the device proper.

It frequently occurs that, during potting, a small quantity of air may become trapped within the space that should ordinarily be occupied by solid insulation. As a rule, this air is under reduced pressure with the result that its breakdown value is far less than is true of air at atmospheric pressure. Hence, arcing is apt to oc-,

our in such pockets with consequent carbonization of insulating material and cumulative breakdown.

Where apparatus is subjected to rapidly varying atmospheric conditions such as occur in the tropics or in aircraft, the problem of effective sealing against weathering is greatly aggravated.

If the seal should happen to be defective, there is a strong probability that moisture will be forced into the pocket or pockets. As a rule, such moisture results in the establishment of a fairly good so conducting path so that breakdown of insulation may occur.

The invention herein provides a lead-in construction whereby the above defects are eliminated. By virtue of the improved construction,

the possibility of air pockets is eliminated while, at the same time, a tight seal is provided. It must be borne in mind in the case of a lead-in seal that thestructure must have sufficient resilience so that mechanical shock will not permanently damage the seal. Thus, in the case of the usual glass lead-in seals, a sharp blow may easily fracture the seal, resulting in permanent damage. By virtue of the invention herein, sufrelatively simple and satisfy the condition that the seal structure be susceptible to quantity production and installation.

The invention herein described meets the above requirement to a high degree. The lead-in structure is relatively simple, requires few parts,

- and telescoping with sleeve ll.

. 2 and may be assembled and installed with the simplest of tools.

For a more thorough explanation of the invention, reference will now be made to the drawing wherein Figure 1 is a top plan view of a construction embodying the invention.

Figure 2 is an elevation along 2--2 of Figure 1.

Figure 3 is an exploded view of the lead-in assembly.

Figure 4 is a sectional elevation showing a modified lead-in.

Figures 5, 6, and 7 are sections on lines 5-5, 6-6, and ll respectively on Figure 4.

The device to which lead-ins are applied may be any apparatus which is desired to seal and, in particular, may be a transformer or any other winding or windings or condenser. In any event, the device may be housed in casing i0, preferably of metal, having apertured cover plate ll. Cover plate H, as shown, may be provided with four lead-ins. Thus cover plate ll may have sunken or recessed portion l2 provided with suitable aperture I! through which each lead-in assembly may be projected.

The lead-in assembly itself may consist of an elongated member which, in its simplest form, may be rivet is having head 16 normally disposed on one side of plate ll within casing l0. Immediately above head l6 and threaded over the body of rivet l5 may be a rigid insulating spacer sleeve l'l formed of Bakelite, fiber or paper or other fairly rigid material and preferably have a high insulating value. Insulating sleeve l'l defines an annular space H around said rivet body. Spacer I! may have fiat bottom face l8 and top face l9 adapted to be adjacent the cover plate with one or lnore slots 20 out in face I9.

Disposed above cover i i is washer 22 of relatively soft material such as neoprene, rubber or leather. Washer 22 is preferably so dimensioned as to fit snugly into recess [2 in cover plate ll. Above washer 22 and telescoping therewith is insulating sleeve 24, which may be of rigid material such as porcelain or glass. Insulating sleeve 24 has reduced portion 25 passing through aperture [3 and extending into annular space ll Shoulder 25' is preferably shaped to slope downwardly toward the outside thereof. Thus soft washer 22 may be crowded in toward the center. The top portion of insulating sleeve 24 is provided with enlarged tapered bore 26, while channel 21 passes through the insulator length. Relatively soft insulating collar 28 of rubber or similar material is adapted to fit within bore 26 and project slightly above the top surface of insulating member 24. It is understood that these various insulating members are threaded on rivet l5.

Above collar 28 is terminal 20 having connecting lug 3|. Terminal 30 is provided with suitable aperture 32 for threading through the upper portion of rivet IS. The body of terminal 30 forms a washer for covering soft collar 28. The entire assembly is compressed, thus urging all the insulating sleeves toward casing wall II and the free end of rivet it turned over to maintain the lead-in assembly in desired position.

In order to establish electrical contact between the device proper such a transformer,

winding and lead-in structure, wire 34 from such device may be threaded into the bore of rivet l5 and soldered in position. The soldering seals rivet l5. It is understood that, instead of a hollow rivet, a solid rivet or even bolt may be used and the soldered connection be made to whatever available surface there is present.

Casing in may be filled with suitable insulating compound 35 such as wax, tar, oil, etc. In order to accomplish this, an aperture 36 may be provided in any suitable portion of the entire container, such as in cover plate ii. Through this aperture, hot insulating compound may be forced under pressure and container l completely filled. Thereafter, aperture 55 may ing.

The potting is carried, out by running into container Ill suitable insulating compound in liquid form when hot. This liquid compound, which may be solid at room temperature, drops to the bottom of the container and, as its level rises, forces air within the container out through aperture 36 or some other air vent. When the level of liquid compound has risen as high as the terminal structure, it has been found that air becomes trapped within annular region ll of collar il. While all trapped air from this region might finally escape if the potting operation were done slowly, the viscosity of the compound and the rapid filling of the container both cooperate to make it difllcult for the trapped air to escape. The trapped air expands with heat from the liquid compound during potting and air is forced out through collar clearances. The remaining trapped air results in a pocket at subatmospheric pressure after. the entire structure has been sealed and has cooled. This reduced air pressure in a pocket in some instances has been instrumental in causing a breakdown of the entire device. Thus an air pocket between rivet l and casing l0 may be in a sufiiciently strong electric field to cause arcing in the air pocket and carbonization of insulating compound.

By providing one or more channels in collar il it has been found that ready access of insulating compound to region i1 is provided and a ready escape for air fromregion I1 is also provided. With the improved structure, hot insulating compound will flow easily into the space between collar ll of compound during potting rises to the lead-in structure and eliminate all possibility of air entrapment. As shown, the compound preferably extends right up to top cover I I of the container.

The trapping of air in the neighborhood of rivet I5 is particularly undesirable, since it is usual for maximum potential gradients to exist between the rivets and top plate ll. Thus, the

and rivet l5 when the levelstances to the utter exclusion of any air or gas.

be sealed by solder- Even if an insulating material like oil, which is normally liquid, is used the trapping of any air is undesirable. Whether the insulating compound is liquid or solid, arcing may occur in the air pocket usually formed.

Referring now to Figures 4-7 inclusive, a

modification is shown wherein the lead-in is locked against rotation relative to the casing structure by positive locking means. Thus, casing 40 may have well 4| with non-circular aperture 42 punched out therefrom. As shown here, aperture 42 is hexagonal. However, other shapes are possible. Porcelain member 43 has reduced extension 44 of non-cicular shape to fit aperture 42. Thus, by providing extension 44 with a hexagonal section, it may be fitted into aperture 42. While the fit does not have to be precise, it should be snug enough so that porcelain 43 cannot be turned in aperture 42.

A rigid insulating sleeve 45 is disposed within casing 40 and is maintained tightly in position by rigid washer 46 and nut 41 on bolt 48. Bolt 48 passes through the lead-in in a manner similar to rivet I5. Bolt 48 carries locking washer 50 above porcelain sleeve 43. Locking washer 50 is adapted to force a soft insulating sleeve 5| into the tapered opening in porcelain sleeve 43. Washer 50 has a plurality of locking projections 52 extending down toward porcelain sleeve 43 and engaging radial locking channels 53 in the top face of sleeve 43. Connecting ing 55 is disposed adjacent locking washer 50 and maintained in position by nut 56.

It isclear that looking washer 50 and lug 55 may be combined into one structure. It is understood that insulating sleeves 45 are provided with channels similar to 20 in part Hi. When the entire lead-in assembly is'tightened up, the structure will remain rotatably locked to casing 40 so that it will withstand substantial mechanical turning movements.

I claim:

1. A sealed lead-in. construction comprising an apertured metallic casing wall having insulating compound on one side thereof and extending substantially to the casing wall and into which the projecting part of the lead-in structure is disposed, an elongated metallic member disposed in said aperture and passing through from one side of the wall to the other side thereof, a first insulating sleeve disposed around said metallic member on one side of said casing wall and having an annular space between the sleeve and member, a second insulating sleeve around said member on the other side of said casing wall, said second insulating sleeve having a reduced extension telescoping to the one side of said casing wall into said-annular space, said two sleeves being of rigid insulating material, a third and resilient insulating sleeve around said member between said casing wall and adjacent end of said second insulating sleeve, a fourth and resilient insulating sleeve around said member adjacent the free end of said-second insulating sleeve, means on the metallic member pressing all sleeves tightly toward said casing wall, means for establishing electrical contact at the ends of said metallic member, said first sleeve having at least one channel to provide a passage from the interior of said sleeve to the exterior thereof,

casing wall is higher than said sleeves hot insleeve and be replaced by insulating compound. 7

2. The structure of claim 1 wherein said metallic member is a hollow rivet and wherein the electrical contact on one side of said casing wall is made on the inside of said rivet for sealing.

3. The structure of claim 1 wherein said metallic member is a bolt, means for locking said second sleeve against rotation with respect to said casing wall, a nut threaded on said bolt adjoining the fourth insulating sleeve, said bolt and nut threads comprising the means for pressing all sleeves tightly toward said casing wall.

4. The structure of claim 1 wherein said apertured wall forms part of a casing having therein an electrical device operating at high potential, and wherein the means for establishing electrical contact at the ends of said metallic' member includes a contact going to said electrical device within the casing and a contact on the exterior of said casing for external connection, said casing bein filled with the insulating com Pound. I

DONALD SCHWENNESEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,766,593 Bramwell June 24, 1930 1,846,447 Millermaster Feb. 23, 1932 1,932,456 Gaston Oct. 31, 1933 2,087,920 Maseuch July 27, 1937 2,348,254 Hartzell May 9, 1944 2,351,543 Race June 13, 1944 2,368,548 Kalstein Jan. 30, 1945 

